Isoolefin polymers, and in particular, hydrocarbon-rubbers, may be prepared in carbocationic polymerization processes. See, e.g., Organic Chemistry, SIXTH EDITION, Morrison and Boyd, Prentice-Hall, 1084-1085, Englewood Cliffs, N.J. 1992, and K. Matyjaszewski, ed, Cationic Polymerizations, Marcel Dekker, Inc., New York, 1996. The catalyst system for producing hydrocarbon-rubbers typically includes two components: an initiator and a Lewis acid. Examples of Lewis acids include AlCl3 and BF3. Examples of initiators include Brønsted acids such as HCl, RCOOH (wherein R is an alkyl group), and H2O. During the polymerization process, in what is generally referred to as the initiation step, the isoolefin, e.g., isobutylene, reacts with the Lewis acid/initiator pair to produce a carbenium ion. Following the initiation step, additional monomer(s) units add to the formed carbenium ion in what is generally referred to as the propagation step. These steps typically take place in a diluent or in a solvent.
Industry has generally accepted widespread use of a slurry polymerization process to produce hydrocarbon-rubbers, using methyl chloride as the diluent. Typically, the diluent used in slurry polymerization processes consists essentially of methyl chloride. Methyl chloride is employed for a variety of reasons, including the ability of methyl chloride to dissolve the monomer(s) and the aluminum chloride catalyst of the reaction mixture, but not dissolve the hydrocarbon-rubber polymer product of the polymerization process. Methyl chloride also has a suitable freezing point to permit low temperature polymerization, typically at temperatures less than or equal to −90° C. Methyl chloride also has a suitably low boiling point to allow for effective separation of the hydrocarbon-rubber polymer from the diluent. A slurry polymerization process using methyl chloride as the diluent also offers the advantage of a hydrocarbon-rubber polymer concentration of approximately 26% to 37% by volume in the reaction mixture, as opposed to a concentration of only about 8% to 12% in a solution polymerization process, wherein the hydrocarbon-rubber polymer is at least partially dissolved in a solvent. Reaction mixtures using methyl chloride as a diluent also have a relatively low viscosity, enabling the heat of polymerization formed during the polymerization reaction to be removed effectively by surface heat exchange.
Typical commercial reactors used to produce hydrocarbon-rubber in a slurry polymerization process include well mixed vessels with a volume of about 10 to 30 liters, wherein the circulation of the reaction mixture is often provided by a pump impeller. An example of such a reactor includes a continuous flow stirred tank reactor (“CFSTR”) as described in U.S. Pat. No. 5,417,930, which is incorporated by reference herein. For purposes herein, a reactor suitable for use in a slurry polymerization process to produce rubber is referred to in general as a “reactor” or as a “butyl reactor”.
Once the hydrocarbon-rubber is produced, at least a portion of the diluent may be removed, and the hydrocarbon-rubber may be transferred from the reaction mixture into a vehicle comprising the hydrocarbon-rubber and a solvent. This vehicle is referred to as a hydrocarbon-rubber cement, or merely as a cement. However, the residual monomer(s) and other impurities present in the reaction mixture may also be transferred into the hydrocarbon-rubber cement. The residual monomer(s) and other impurities are known to negatively effect subsequent processing of the hydrocarbon-rubber. It has long been recognized that substantial economies in polymer processes, improved physical properties of the hydrocarbon-rubber, as well as cost and processes savings related to the slurry polymerization process could be achieved by removing residual monomer(s) and other impurities from the hydrocarbon-rubber cement.
Other background references of interest include U.S. Pat. Nos. 2,542,559; 2,940,960; 3,553,156; 3,470,143; 3,496,135; 3,726,843; 4,623,712; 4,857,633; 5,264,536; 5,624,878; and 5,527,870; U.S. Patent Application US2004/0119196A1; RU 2 209 213; DE 100 61 727 A; EP 014 934 2 A2; WO 02/096964; WO 02/34794; and WO 00/04061.